Method of and apparatus for generating and superheating steam



May 26, 1931. w, 5, BUELL 1,807,505

METHOD OF AND APPARATUS FOR GENERATING AND SUPERHEATING STEAM Fiied.April 25, 1922 Patented May 26, 1931 UNITED STATES.

PATENT; OFFICE WALES S. B'OELL, OF BROOKLYN, NEW YORK, ASSIGNOR TOFOSTER WHEELER COR- PORATION, or NEW YORK, N. Y., A

CORPORATION OF NEW YORK METHOD OF AND APPARATUS FOR GENERATING ANDSUPERHEATING STEAM Application filed April 25,

The present invention relates to the generation and superheating ofsteam and is characterized by the absorption of radiant heat from thecombustion chamber of a boiler furnace by which the steam is generatedto obtain a substantial portion, usually 50% or more, of the totaldesired superheating effect, and by obtaining the remainder of the heatutilized in superheating the steam wholly or mainly'by contact with andconduction from the boiler furnace heating gases after the latter havebeen cooled somewhat by cont'act with heating surface of the boilerproper, so that the tendency for the degrees of superheat secured by theabsorption of radiant heat to diminish as the amount of steam generatedincreases and as the amount of excess air from the heating gasesincreases, is neutralized wholly or in large part by the tendency of thedegrees of superheat furnished by heat abstracted from the partiallycooled heating gases to increase as the rate of steam generationincreases and as the rate of excess air in the heating gases increases.

In the practical carrying out of the invention, the radiant heatsuperheating effect is obtained by means of a so-called radiant heatsuperheater exposed to the interior of the boiler combustion chamber andordinarily incorporated in the wall thereof, and disposed out of thepath offlow of any considerable portion of the heating gases so as tominimize the heat absorption of this superheater by contact with andconduction from the heating gases as well as to minimize the oxidizingeffect of the heating gases on the superheater. The remainder of thedesired superheating effect is obtained by means of a suitablyproportioned ordinary superheater in the path of .the heating gasesleaving the combustion chamber and contacted by the latter after theyhave passed over more or less of the boiler heating surface and havebeen correspondingly cooled.

The manner in which the two superheaters arranged asdescribed cooperateto secure a more uniform degree of superheat than can be obtained witheither, and particularly with the radiant heat superheater, when usedsuperheating effect of the pends both crease in the boiler load 1922.Serial No. 556,372.

boiler furnace the rate of fuel combustion must be Varied eithermanually or automatically in general accordance with the boiler load, i.e. the vrate at which steam is generated and withdrawn from the boiler,and the weight of the heating gases therefore varies in approximateproportion to-the boiler load, though ordinarily the proportion is notexact because the furnace chamber tempm'ature increases somewhat as theload increases and in practice the combustion efficiency is usuallysomewhat higher at heavy boiler'loads than at light loads. I11 eithertype of superheater the degrees of superheat imparted to the steampassing through the superheater depends of course on the amount of heatabsorbed by the superheater and on the amount of steam to be therebysuperheated, In the radiant heat superheater the rate of heat absorptiondepends almost entirely on the furnace chamber temperature, and theeffect of an increase or decrease in boiler load is to respectivelyreduce or increase the degreesof superheat because the change in theamount of steam to be superheated is substantiall greater than theeffect on the amount of heat absorbed of the relatively small changes infurnace chamber temperature occurring as a result of changes in the rateof combustion. Since the effect of an increase in the amount of excessair in the heating gases is to lower the furnace chamber temperature aswell as the temperature of the heating gases, the

radiant heat superheater diminishes and increases as the amount ofexcess air increases and'diminishes. V

In the case of the superheater heated by contact with and conductionfrom the heating gases, the rate of heat absorption deon the weight ofthe heating gases sweeping over the superheater and on the temperatureof those gases. With an inthroughout what may be regarded as a normalload variation, say from 50% to 200% of rating, the degrees of superheatgiven the steam by this superheater increases, for while the effect ofthe increased weight of heating gases is substantially neutralized bythe increased weight of steam to be superheated, the gases come to thesuperheater at increasingly higher temperatures as the load increases.

In practice at a certain high boiler load which is different fordifferent conditions, the superheat furnished by the ordinary gascontact heated superheater reaches a maximum and then diminishes as theload is further increased. This results primarily from the fact that thehigher loads can be carried only with an amount ofexcess air in theheating gases less than ordinarily exists at lighter loads, though thefact that at the higher boiler loads the rate of increase in temperatureof the heating gases reaching the superheater diminishes, may alsocontribute: to the decrease in superheat at very high boiler loads. Theeffect of an increase or decrease in the amount of excess: air on thegas contact heat superheater is to respectively increase or decrease thedegrees of superheat obtained, because the change in the than whenobtained by a weight of heating gases flowing past. the superheater is amore important factor in this connection than is the correspondingchange in heating gas temperature. Thus throughout the normal range ofboiler load variation the effect of a change in the boiler load on thesuperheating effect of one superheater is neutralized or compensated forin whole or in part by the corresponding change in the superheatingeffect of the other superheater and this is true also of the effect onthe superheaters of a change in the percentage of excess air supplied tothe furnace.

The relative portions of the total superheating effect furnished by thetwo superheaters which will give the best results from a practicalstandpoint vary with conditions, and depends in part on suchconsiderations as the relative cost of construction and maintenance ofthe two types of superheaters and the space conditions in the boilerfurnace installation. The radiant heat superheater requires less heatingsurface and ordinarily is less expensive to construct and maintain thanan ordinary su erheater giving the same superheating e ect and hence itis ordinarily desirable from a practical standpoint to obtainas much ofthe superheating effect with the radiant superheater as is possible,consistent with the reguired degree of uniformity in superheat un ervarying conditions of load and combustion efficiency, though in someinstallations, the construction cost of the superheater provisionsrequired for a given superheating effect may well be less when thiseffect is obtained with two small superheaters, one of each type singlelarge superheater of either type.

This is due to the fact that the effectiveness and hence theconstruction cost per unit of capacity with each type of superheaterdepends upon its location in the boiler settin The most favorablelocation for the ra iant heat superheater is in the zones of the furnacewalls receiving the maximum radiation. These zones are comparativelynarrow and when the radiant heat superheater capacity required isrelatively large, these zones may not be large enough to receive all ofthe superheater surface, and the portions of said surface than locatedoutside of those zones are much less effective than in some cases notmore than one quarter as effective as, portions of similar area in thehigh temperature zones. The most effective location for an ordinary orgas contact heated superheater is that in which the superheater is sweptby heating gases which have traversed only a small portion of the boilerheating surface and have been cooled only as little as is necessary topermit them to come into contact with the superheater without unduedeterioration of the latter. This most favorable location is ordinarilytoo small to receive more than a comparatively small sized superheater.An ordinary superheater located near the combustion chamber will give asuperheating effect which varies less on changes in boiler load than isthe case with the radiant heat superheater, though when the ordinarysuperheater is located relatively near to the oiler stack outlet, thevariation in its superheating effect as a result of changes in boilerloads is more marked than in the case of the radiant heat superheater.In practice however, it is not usually possible to obtain a highsuperheating effect, say 200 F. or above, with an ordinary superheaterinstalled in a water tube boiler of large capacity such as is nowgenerally used in lar e power stations, because there 1s not availa lespace for the location of an adequate amount of superheating surfaceclose to the furnace chamber, and when located at a point nearer thestack where more space is or may be made available, the increased amountof superheater surface required entails a prohibitive cost ofconstruction.

Proposals have heretofore been made to employ two superheater-s in asingle boiler in such fashion that one superheater would, and the otherwould not receive some radiant heat, but in such proposals there hasbeen no thought of obtaining the uniformity in superheat which issecured with the arrangement herein described, and the superheaterreceiving radiant heat has been disposed and intended to be heatedlargely by contact with-and conduction from the heating gases, therebymaking the variation in its superheater effect on changes in the boilerload or combustion conditions an uncertain quantity. Moreover, asuperheater exposed to a vigorous flow of burning gases at thecombustion chamber temperature is subject to a much more severedeteriorating effect than is a superheater out of the path of flow ofsuch gases though exposed to the same temperature, and a superheaterheated wholly or mainly by radiant heat may be constructed in a mannerbetter adapting it to resist the deteriorating conditions to which it issubjected than is possible with a superheater intended to receive muchof its heat by contact with and conduction from heating gases.

In the accompanying drawings and descript-ive matter I have illustratedand described one embodiment of my invention in a boiler of one of themany types with which the invention may be carried out. The embodimentillustrated also comprises certain novel details'of combination.

Of the drawings:

Fig. 1 is a general sectional view of a boiler showin the twosuperheaters combined therewi i.

Fig. 2 is a section on the line 2-2 of Fig. 1.

Fig. 3 is an enlarged side elevation of the radiant heat superheater.

The boiler here shown is of the' Stirling or Connelly type, and containsan ordinary or standard superheater 1, located back of the first bank ofboiler tubes and provided with the Foster type of superheater rings.There is also installed in the front wall of the fire chamber 2 aradiant heat superheater 3, which is connected in the series with thesuperheater 1 by the connection 4. Steam from the boiler passes firstthrough superheater 1 and then through superheater 3, the outlet headerof the latter being indicated at 5.

The radiant heat superheater is composed of tubes 6 encased in cast ironenvelopes 7 which are separated by refractory blocks 8. L-shaped bars orplates 9, (preferably of steel) are embedded in the front walls andserve as supports or stifi'eners for the iron encased superheater tubeswhich at intervals are bolted to said plates as shown at 10.

Preferably the connecting conduit 4 between the two superheaters isdisposed as shown and extends up to a point above the water level in theupper drums. This enables the radiant heat' superheater to be flooded instarting up the boiler without flooding the upper superheater 1 and without requiring the use of a valve between the two superheaters. Suchflooding is usually effected to prevent destructive heating of theradiant heat superheater until the boiler is connected to the steamline.

As indicated above, space limitations, commercial considerations, andload or combustion conditions, mitigate against the use of either astandard or a radiant heat superheater in such boilers as the oneillustrated, of sufficient capacity to be used alone, but the tworelatively small superheaters arranged as set forth will, in theaggregate, meet all practical requlrements, besides yielding a uniformsuperheat.

Having now describedv my invention, What I claim is:

l. The method of generating and superheating steam characterized by thedirect absorption by metallic bodies of radiant absorption by metallicbodies of radiant heat from the combustion chamber to the boiler furnacein which the steam is generated to furnish a substantial portion of thedesired superheating effect, and by the absorption of the additionalheat required for the super-heating effect, wholly or largely from theheating gases leaving said combustion chamber after the latter have beenpartially cooled by contact with the water heating surface of theboiler, to thereby neutralize or compensate to a substantial degree forthe decreases in the superheating effect due to radiant heat which occurwhen the rate of steam generation or the amount of excess air suppliedto the furnace increases, by the increase in superheating effect due tothe heat abstracted from the partially cooled heating gases occurring onan increase in boiler load or in the amount of excess air.

3. Apparatus for generating and superheating steam comprising a watertube boiler and its furnace, a superheater having exposed metal wallslocated in position to absorb heat substantially solely by radiationfrom the combustion chamber of the boiler furnace, a second superheaterlocated in position to absorb heat by contact with the boiler heatinggases after the latter have been partially cooled by contact with theheating surface of the boiler proper, and connections for passing thesteam generated in the boiler through both superheaters whereby therelative decrease in superheating effect of the firstmentionedsuperheater resulting from an increase in the rate of steamgeneration or in the amount of excess air supplied to the furnace isneutralized or compensated for by the simultaneous increase furnish aportion of the desired superheatv absorb heat mainly by in relativeheating effect of the second superheater.

4. Apparatus for generating and superheating steam comprising a watertube boiler and its furnace, a superheater having exposed metal wallslocated out of the main path of heating gas flow, but in position toradiation from the combustion chamber of the boiler furnace, a secondsuperheater located in position to absorb heat by contact with theboiler heating gases after the latter have been partially cooled bycontact with the heating surface of the boiler proper, and connectionsfor passing the steam generated in the boiler through both superheaterswhereby the rel- 'ative decrease in superheating effect of the firstmentioned superheater-resulting from an increase in the rate of steamgeneration or in the amount of excess air supplied to the furnace isneutralized or compensated for by the simultaneous increase in relativeheating effect of the second superheater.

5. Apparatus for generating and superheating steam comprising a watertube boiler of the Stirling type and its furnace,

a superheater having exposed metal walls located in the, front wall ofthe combustion chamber of the furnace and adapted to absorb heat whollyor mainly by radiation from the combustion chamber of the boiler furnaceand a second superheater located between the first and second banks ofboiler tubes.

6. Apparatus for generating and superheating steam comprising a watertube boiler and its furnace, a superheater located in the path of theheating gases after the later have traversed a portion of the boilerheating surface, a second superheater located out of the main path ofheating gas flow, but in position to absorb heat mainly by radiationfrom the combustion chamber of the furnace, and means for passing thesteam withdrawn from the boiler first through one and then through theother superheater, said means comprising a condult connecting thesuperheaters and including a portion extending upward from the secondsuperheater to a level above the boiler water level whereby the fillinof said second superheater with water wil not flood the first mentionedsuperheater.

In testimony whereof I hereto afiix my signature WALES S. BUELL.

